重新审视大地电磁理论：层状感应与地电场
Revisiting magnetotelluric theory: layered induction and geoelectric fields
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中文总结 AI 辅助
本文重新审视水平分层地球的大地电磁理论，推导扩散近似与阻抗递推，并通过三次评估验证层状模型在计算地电场中的准确性，发现其优于磁场重建和克里金插值方法。
中文摘要 AI 辅助
我们回顾了平面波强迫下水平分层地球的大地电磁（MT）理论及其在地电场计算中的应用。从麦克斯韦方程组出发，通过在层边界匹配电场和磁场，推导了扩散近似和阻抗递推关系。等效传输线将表面阻抗与随深度的衰减、视电阻率、相位以及磁场时间序列的电场响应联系起来。推导过程伴随三次评估，每次均针对各自的参考标准。首先，在2024年5月10日至11日的磁暴期间，根据拟合实测阻抗张量的层状模型计算出的电场，与根据张量直接计算出的电场相比，在1614个具有足够周期覆盖的EarthScope MT台站上，中值矢量误差为46%。仅将每个张量简化为其反对称投影，中值误差为46%，而层状拟合和数值处理的中值误差分别为1.9%和1.3%。其次，在20个 withheld 观测站中，利用剩余网络重建的磁场，其中值矢量误差为48%。在常见的电场比较中，磁场重建在32,280个观测站-张量对中的96%中产生更大的电场矢量误差，中值分别为93%，而层状表示的中值为46%。第三，当通过克里金插值将MT台站推断的电导率插值到 withheld 区域时，预测阻抗的中值相对误差为57.3%，149个 withheld 台站中有11个在一个或多个周期上的视电阻率差异达到100倍或更多。矢量比较保留了电场幅度和方向的差异，这些差异对于计算输电线路沿线的感应电压至关重要。
英文摘要
We review the magnetotelluric (MT) theory of a horizontally layered Earth under plane wave forcing and its use in calculating geoelectric fields. Starting from Maxwell's equations, we derive the diffusion approximation and the impedance recursion by matching electric and magnetic fields at layer boundaries. The equivalent transmission line connects the surface impedance to attenuation with depth, apparent resistivity, phase, and the electric response to a magnetic time series. Three evaluations accompany the derivation, each against its own reference. First, under the storm of 10 and 11 May 2024, electric fields calculated from layered models fitted to measured impedance tensors differ from those calculated from the tensors by a median vector error of 46% across 1614 EarthScope MT sites with sufficient period coverage. Reducing each tensor to its antisymmetric projection alone gives a median of 46%, while the layered fit and numerical processing give medians of 1.9% and 1.3%. Second, the magnetic field reconstructed at each of 20 withheld observatories from the remaining network has a median vector error of 48%. In a common electric field comparison, the magnetic reconstruction gives the larger electric vector error in 96% of 32,280 observatory-tensor pairs, with medians of 93% against 46% for the layered representation. Third, when conductivity inferred at MT sites is interpolated by kriging into withheld regions, the median relative error of the predicted impedance is 57.3%, and 11 of 149 withheld sites have an apparent resistivity discrepancy of a factor of 100 or more at one or more periods. The vector comparison retains differences in the amplitude and direction of the electric field that are relevant to calculating induced voltages along transmission line routes.
